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    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>2021-03-29</title>

    <!-- script 标签不用写 type 属性也可以 -->
    <script>
        // 变量
        var a
        a = 'Hello World!'

        // 调试
        // alert(a)
        // document.write(a)
        // console.log(a)
        // console.log(a)


        var b
        console.log(b) // undefined

        // boolean
        var d
        if (d === true) {
            console.log('真')
        } else {
            console.log('假')
        }

        // isNaN
        console.log(isNaN(67)) // false
        console.log(isNaN('67')) // false
        console.log(isNaN('6d7')) // true


        // Object
        var a = new Object()
        var b = new Object(88)
        c = new Object() // 允许，但不建议
        d = new Object  // 如果无参，参数列表可以省略，不推荐

        console.log(a, b)

    </script>
</head>
<body>

</body>
</html>
